Abstract:

In Beijing Dongling Mountainous area, the coppiced populations of Liaodong oak (Quercus wutaishanicaMayr) usually appear as an associated tree species of the Chinese pine (Pinus tabulaeformis Carr.) artificial forest. In some places the artificial pine forest is replaced by mixed crops of Chinese pine and Liaodong oak, or the oak takes the place of the pine as the dominant species in some specific habitats along the ridges and the upper slopes of hills. In order to compare and understand the recruitment and establishment of Liaodong oak seedlings under Chinese pine artificial forest as well as the natural regeneration mechanism of the oak forest, an artificial forest of Chinese pine with Liaodong oak as an associated species in Beijing Dongling Mountainous area was selected, and comparative experiments on the recruitment and establishment of seedlings were conducted by sowing the acorns of Liaodong oak about 2 cm below the floor surface in two habitats, under the canopies and along the boundaries of the artificial forest. The results showed that in the mast year of the oak, though the difference of loss of the acorns planted in these two habitats was not significant, yet there were highly significant differences in the recruitment and establishment of seedlings. Since activities of small forest animals, rodents in particular, have both positive and negative effects on oak forest regeneration, through acorn consumption and germination facilitation, close attention was paid to the phenomenon of cotyledon loss of acorns and the consequences of the loss. As the acorns germinated as soon as they fell from the mother tree in autumn, before the seedlings sprouted their caudices, the taproots would have grown 10_20 cm long and formed primary root systems, implying that certain amount of the nutrition stored in the cotyledons had been transported to the roots. From the field experiments it was found that the acorn cotyledons were consumed by the predator in three ways during the early seedling stage: 1) the seedlings lost their cotyledons without harming any other parts, which often occurred along the forest boundaries, accounting for 29.69% of the germinated acorns; 2) the whole seedlings were drawn out of the soil, which almost always happened under the forest canopies, accounting for 62.43%; 3) the stems of seedlings were broken at the bases where the cotyledons are connected, occurring 50.88% along the boundaries, more frequently than under the forest canopies where only 8.41% of germinated acorns occurred. Only the latter two ways caused the seedlings to die, while cotyledon loss after seedling emergence from the soil had little negative effects on the growth and survival of the seedlings. These phenomena might result from different soils between these two habitats; soil along the boundaries has little humus and is much harder and drier than that of the forest floor under the canopy. Also, the taproots were much longer along the boundaries. So when rodents predate the seedlings along the boundaries, it would be easier to split the cotyledons from the seedlings instead of pulling out the whole root from the soil. At the end of the first living period, the survival rate of the seedlings along the boundaries was close to 20%, the average height of the stems reached 7.94 cm, average buds were 11.24 per seedling, and the average dry weight of leaves was 81.14 mg per seedling. Moreover, almost all of the surviving seedlings along the boundaries lost their cotyledons. The survival rate under forest canopies was less than 2%, the average height of stems reached 4.74 cm, average buds were 7.52 per seedling, and the dry weight of leaves was only 42.27 mg per seedling, but the surviving seedlings under canopy did not lose their cotyledons. The above results showed that the habitats along the forest boundaries and similar areas would be more beneficial to the recruitment and establishment of oak seedlings.